The present invention relates to quickly-attachable pipe couplings, and particularly to a coupling for use in coupling either two rigid pipes together, or one rigid pipe to a flexible tube.
Pipe couplings are known in the art comprising a metal band wound around a flexible pipe or tube and tightened, usually by means of a screw mechanism, for clamping the flexible tube to a rigid pipe with sufficient pressure to prevent leakage of fluid therefrom. The flexible tubes commonly used in such couplings may be made of natural or synthetic rubber or plastics, and are commonly referred to as elastomer tubes to indicate their elasticity, flexibility, and compressibility characteristics. By using a short length of the flexible tube having a hose clip or metal band at each end, they may be used to couple two rigid pipes together, one clip or band clamping the flexible tube to one pipe, and the other clip or band clamping the tube to the second pipe.
Among the major disadvantages of such pipe couplings as known in the art are: (a) the installer does not know how much compression to apply, since if too little is applied it can result in a weak coupling or leakage, and if too much is applied, it can cause irreversible damage to the elastomer tube; (b) the elastomer tube tends to take a permanent set, i.e. it tends to "flow" so that the compression that it applies to the rigid pipe gradually is diminished, this leading to a weakened coupling and the possibility of leakage; and (c) exposed portions of the elastomer may deteriorate because of ultra-violet radiation (in sunshine) or other combined atmospheric and radiation effects.
Another known form of pipe coupling includes a piece of spring wire, usually of circular cross-section and having a little more than one turn, with ears extending from the ends to permit the turn to be expanded--so as to slip over the elastomer--and then close down by the elastic forces. This type of coupling suffers from the same disadvantages as the first form, except that the pressure applied is not controlled by the installer. On the other hand, the narrow form of these clips can result in cutting of the elastomer (i.e. a short life for the system) and in a tendency for the rigid pipe to pull-out of the coupling when high internal pressure produces an axial force on the pipe. This force (B) may be expressed by the equation B=.pi.D.sup.2 P, where "D" is the diameter of the pipe, and "p" is the pressure of the fluid in the pipe. This force must be resisted by the friction of the elastomer on the tube, i.e. .pi.Dl.mu.P, where ".mu." is the coefficient of friction between the elastomer and the pipe, "P" is the compression force per unit area, and "l" is the length of the elastomer which is under compression. Thus, ##EQU1##
Since, in these types of couplings, "l" is usually less than D/4.mu., it is necessary to use a compression force "P" considerably greater than "p".
An object of the present invention is to provide a new form of pipe coupling having advantages in the above respects over both of the above known types of couplings, and which has the further advantage of permitting its quick attachment to the pipe or pipes to be coupled.